Image processing apparatus

ABSTRACT

Black inverted noises in a white background due to resolution correction are reduced by an image processing apparatus which carries out image modification processing to invert at least a portion of a binary converted signal obtained from binary conversion of an image signal. An image signal S 1  is respectively input to resolution correction means  201  and  202  using different correction amounts. The signal is then input to selecting means  310  from the both resolution correction means. The signal output from the selecting means is input to binary conversion means  400  and a signal S 2  output therefrom is input to image modification processing means  500 . when image modification processing has been instructed, a control signal CNT 1  is input to the selecting means  310  and the selecting means output a signal with weak resolution correction from the resolution correction means  202  using a small correction amount.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image processing apparatus, and morespecifically, to a measure to cope with noises generated by an imageprocessing apparatus which carries out image modification processing toinvert at least a portion of a binary signal obtained through binaryconversion of an image signal on which resolution correction forimproving spatial resolution has been carried out.

2. Description of the Related Art

An image inputting apparatus has been known which obtains an imagesignal carrying image information of an original by scanning theoriginal with an image sensor or the like and converting the originalimage into an electric signal (for example, a scanner, or a stencilmaking apparatus). To improve optical resolution, it is general for suchan image inputting apparatus to carry out resolution correction forimproving the spatial resolution of an image (for example, MTFcorrection) on an image signal having been obtained.

After an image signal have been binary converted, if the image whereinwhite pixels are scarcely seen in a black pixel dominant area (a blackpixel area) is printed by a printer for example, the white pixels in theblack pixel area are not so conspicuous. However, when such an image isprinted by a printer after inversion processing or inside whiteningprocessing has been carried out thereon, black pixels which have beeninverted from scarce white pixels in a white pixel dominant area (awhite pixel area) which has been inverted from the black pixel areabecome conspicuous. This visual phenomenon has been known.

FIG. 10 is a diagram showing this visual phenomenon and shows a relationbetween the human visual sense and a ratio of black pixels within anarea printed by a printer. In the area where black pixels are dominant(a portion to the right in the figure), the ability to identify apredetermined number of white pixels (A) therein is low and the whitepixels are not conspicuous. In the area (a portion to the left of FIG.10) where black pixels are scarce, that is, the area wherein whitepixels are dominant, the ability to identify the same number of blackpixels (B) therein is high and the black pixels are very conspicuous.

Especially in stencil making printing for example, the finish itself ofprinting tends to extend areas of black pixels due to an effectso-called smear of ink. Therefore, black pixels in a white pixeldominant area become much more conspicuous.

When MTF correction is carried out on an image signal, the abovephenomenon becomes more conspicuous. This is because that a white noisesignal mixed with an image signal output from an image sensor or thelike and having the density of black becomes too enhanced by binaryconversion to be at the level of white after MTF correction has beencarried out on the image. Therefore, in some cases, after binaryconversion has been carried out on a signal having been MTF correctedand a predetermined area has been specified by a digitizer or the like,if signal inverting processing (hereinafter called image modificationprocessing), for example inversion processing and inside whiteningprocessing on the signal in the predetermined area or hatchingprocessing on the area whose inside has been whitened, is carried out onat least a portion of the signal having been binary converted, a portionof the image in the predetermined area which should be inverted fromblack to white is not inverted and remains black. As a result, blacknoises in white background become conspicuous.

Hereinafter, the reason why this phenomenon becomes conspicuous afterbinary conversion has been carried out on a signal having been MTFcorrected. MTF correction will first be explained briefly. FIG. 11 showsa general MTF correction method. In this MTF correction, the value of atarget pixel A to be processed is doubled (D=A×2). A value E which is asum of the values B and C of pixels neighboring with A in the horizontal(main scanning) direction (E=B+C) is divided by 2 to make F (F=E÷2), andF is subtracted from D to make G (G=D−F). In this manner, when the valueA of the target pixel is different from the values of neighboring pixelsB and C, the value A is changed to a larger one if A is larger thanthose, and to a smaller one if otherwise. Therefore, by sequentiallyapplying this MTF correction along the main scanning direction, opticalresolution along the main scanning direction can be improved maintainingthe average (the average density) of the values in the image signal. Itis needless to say that vertical optical resolution can be improved aswell by applying this correction to pixels neighboring with the targetpixel in vertical direction.

The phenomenon in which black pixels due to a noise signal are createdby inversion processing on a signal having been MTF corrected will beexplained next. FIG. 12 shows an example of inversion processing. Thebasis of the inversion processing is to carry out logical inversion on atarget pixel A before processing. In the block diagram and logicexpression in FIG. 12, a circuit for selecting whether to carry outinversion processing is further added to the above basis.

By carrying out this inversion processing, processing shown at thebottom of FIG. 12 corresponding to a selecting signal C from theselecting circuit is carried out on the target pixel A before inversion.In the case of non-inversion (the selecting signal C is 0), a targetpixel D after the processing has the same logic as the target pixel Abefore the processing, while in the case of inversion (the selectingsignal C is 1), the target pixel D after the processing has the logicinverted from that of the target pixel A before the processing. The casewhere this inversion processing is actually applied to an image signalwill be explained next.

An image signal carrying image information of an original is obtained byscanning the original by using an image sensor and converting theoriginal image into an electric signal, and the image signal isconverted from analogue to digital by using an A/D converter. An exampleof the values of the digital signal is shown as a table in FIG. 13(A).In FIG. 13(A), the value 60 of a pixel K3 is a little smaller than thevalue 80 of the surrounding pixels, and shows a small noise component.However, when binary conversion is carried out on these pixels whereinthe values 50 or smaller are converted to white pixels, both the pixelK3 and the surrounding pixels are binary converted to black pixels.Therefore, the pixel K3 does not turn out to be a noise which can berecognized as a white pixel in a black pixel area. Consequently, whenthe inversion processing is carried out thereon, the pixel K3 becomes awhite pixel and it does not turn out to be a noise recognized as a blackpixel. However, when the inversion processing is carried out after theMTF correction on the pixels, the pixel K3 becomes a black noise pixel.

The values after MTF correction carried out on the signal shown in FIG.13(A) are shown as a table in FIG. 13(B). As shown in FIG. 13(B), thevalue of the pixel K3 has changed from 60 to 40 after the MTFcorrection, and the effect as a noise is greater than before thecorrection.

FIG. 14(A) is a table showing data after binary conversion on the signalin FIG. 13(B) wherein the pixels having the values 50 or smaller havebeen converted into white pixels and the pixels having the values largerthan 50 have been converted into black pixels. The noise component inthe pixel K3 is recognized as a white pixel in an area of black pixels.

FIG. 14(B) shows a table after inversion processing on the pixels inFIG. 14(A), and FIG. 14(C) shows a visual expression of the pixels inFIG. 14(B). As shown in FIGS. 14(B) and 14(C), the pixel K3 becomes awhite pixel if no MTF correction has been carried out thereon, while itbecomes a black pixel after the MTF correction. As a result, this blackpixel becomes conspicuous.

The process through which a black pixel due to a noise signal is createdby carrying out inside whitening processing on a signal after MTFcorrection is explained next. The process through which data after MTFcorrection are created is the same as in the explanation of theinversion processing in FIG. 12. FIG. 15 shows an algorithm of theinside whitening processing.

In the inside whitening processing, a cross-shape filter (+) composed ofpixels B and C in vertical direction, pixels D and E in horizontaldirection, and a target pixel A before processing at the center of these4 pixels is applied sequentially to image data. When the pixels D and Eneighboring with the target pixel A in the horizontal direction and thepixels B and C neighboring with the target pixel A in the verticaldirection are all black pixels (the pixel arrangement in this state iscalled inside whitening processing target), a target pixel K after theprocessing is forced to be white regardless of the logic (whether thetarget pixel is a white pixel or a black pixel) of the target pixel Abefore the processing. This is the basic processing of the insidewhitening processing. A circuit for selecting the inside whiteningprocessing is added to the inside whitening processing shown as a blockdiagram and a logic expression in FIG. 15.

Through this inside whitening processing, the processing shown in FIG.16 is carried out on the target pixel A before the processing inresponse to the neighboring pixels B through E and a selecting signal Jfrom the selecting circuit. For a pixel pattern shown in FIG. 16(A), inthe cases of upper edge judgment (a pixel c2 above a target pixel c3 iswhite; B=0), lower edge judgment (a pixel c7 below a target pixel c6 iswhite; C=0), left edge judgment (a pixel a5 to the left of a targetpixel b5 is white; D=0), and right edge judgment (a pixel f5 to theright of a target pixel e5 is white; E=0), the target pixels c3, c6, b5and e5 after the processing are not white. However, if they are in thestate of the inside whitening processing target (see FIG. 16(F)), atarget pixel d4 after the processing is forced to be white sinceneighboring pixels c4 and e4 in the horizontal direction and d3 and d5in the vertical direction are all black. In the logic expressions inFIGS. 16(B)-(F), black pixels are expressed as 1 and white pixels are 0.

The cross-shape filter in the above explanation having reference pixelsand the target pixel in its center has only one pixel in each direction(upper, lower, left, and right) and the border after the insidewhitening processing has the thickness of one pixel. However, byextending the range of the reference pixels in each direction (to makethe cross-shape enlarged in each direction), the border after the insidewhitening processing can be thickened.

FIG. 17(A) is a table showing data wherein the data after the MTFcorrection shown in FIG. 14(A) have been binary converted to white ifthe values are 50 or smaller and to black if otherwise and insidewhitened thereafter. FIG. 17(B) shows a visual expression of the data.As shown in FIGS. 17(A) and 17(B), the target pixel K3 before the insidewhitening processing appears to be a mere white pixel, while it becomesvery conspicuous after the inside whitening processing, because pixelssurrounding K3 generate more black pixels than in the above inversionprocessing, due to the inside whitening processing algorithm.

SUMMARY OF THE INVENTION

The present invention has been created based on consideration of theabove problems. Its object is to provide an image processing apparatuswhich does not generate black pixels (black noises) having beendescribed above, even in the case where resolution correction forimproving spatial resolution of an image has been carried out on theimage and binary conversion and subsequent image modification processingsuch as inversion processing or inside whitening processing are carriedout on the image signal.

An image processing apparatus related to the present invention hasresolution correction means which carries out resolution correction onan image signal to improve spatial resolution of an image, binaryconversion means which carries out binary conversion on the image signalwhose resolution has been corrected by the resolution correction means,and image modification processing means which carries out imagemodification processing to invert at least a portion of the image signalhaving been binary converted by the binary conversion means based on apredetermined instruction, and is characterized by that the imageprocessing apparatus comprises correction amount changing means whichmakes a correction amount of the resolution correction by the resolutioncorrection means small based on the predetermined instruction.

The “image modification processing wherein at least a portion . . . isinverted” means processing which can generate an inversion noise bycarrying out processing such as inversion, inside whitening, andhatching of the area whose inside has been whitened by the insidewhitening processing on a signal obtained by binary conversion of theimage signal after the resolution processing thereon. The imagemodification processing includes not only the processing on an imagesignal for the entire area but also the processing on an image signal ina desired area having been set. Hereinafter, the “inversion noise” meansthe noise appearing as black dots on a white background caused by theimage modification processing.

The “predetermined instruction” means an instruction to order carryingout image modification processing, and the instruction may include areaspecification.

To “make the correction amount . . . small” means to make the degree ofthe resolution correction (the correction amount) small, and includesthe case of no correction (i.e., the correction amount is 0).

The correction amount changing means in the above image processingapparatus is meant to comprise two resolution correction means whichhave different correction amounts for the resolution correction, andselecting means which selects one of image signals whose resolution hasbeen corrected by the two resolution correction means. The selectingmeans can select the image signal with a smaller correction amountbetween the image signals whose resolution has been corrected by the tworesolution correction means, based on the predetermined instruction.

The correction amount changing means comprises the two resolutioncorrection means which use different correction amounts for theresolution correction, two binary conversion means which carry outbinary conversion on each of the image signals whose resolution has beencorrected by the resolution correction means, and selecting means whichselects one of the image signals having been binary converted by thebinary conversion means. Between the image signals whose resolution hasbeen corrected by the two resolution correction means, the selectingmeans selects the binary converted signal with a smaller amount ofcorrection based on the predetermined instruction.

The correction amount changing means may comprise resolution correctionmeans whose correction amount can vary.

Furthermore, the correction amount changing means may change thecorrection amount small for the image signal composing an entire image,based on the predetermined instruction. Alternatively, the correctionamount changing means may change the correction amount small only for aportion of the image signal in an area instructed by the predeterminedinstruction. The “image signal composing an entire image” means an imagesignal which this image processing apparatus can handle at one time,such as an image signal corresponding to a page which can be specifiedby a digitizer at once.

Furthermore, an image processing apparatus related to the presentinvention has resolution correction means which carries out resolutioncorrection on an image signal for improving spatial resolution of animage, binary conversion means which carries out binary conversion onthe image signal whose resolution has been corrected by the resolutioncorrection means, and image modification processing means which carriesout image modification processing to invert at least a portion of theimage signal which has been binary converted by the binary conversionmeans based on a predetermined instruction, and is characterized by thatthe image processing apparatus comprises:

two resolution correction means using different correction amounts forthe resolution correction;

two binary conversion means which carry out binary conversion on each ofthe image signals whose resolution has been corrected by the tworesolution correction means;

image modification processing means which carries out image modificationprocessing only on a binary converted signal with a smaller amount ofresolution correction between the image signals whose resolution hasbeen corrected by the two resolution correction means, and

selecting means which selects either the image signal on which imagemodification processing has been carried out by the image modificationprocessing means or the binary converted signal with a larger amount ofcorrection between the image signals whose resolution has been correctedby the two resolution correction means, and also characterized by that

the selecting means selects the image signal on which the imagemodification processing has been carried out by the image modificationprocessing means based on the predetermined instruction.

In this image processing apparatus, based on the predeterminedinstruction, the selecting means may select the image signal composingan entire image or a portion of the image signal for an area instructedby the predetermined instruction, on which the image modificationprocessing has been carried out by the image modification processingmeans.

In any of the above image processing apparatus comprising the “tworesolution correction means”, in the case of “without correction”, thecorrection amount for one of the resolution correction means may be 0,or one of the resolution correction means for “without correction” doesnot exist and the signal may pass the portion equivalent to theresolution correction means for without correction.

When the image processing apparatus of the present invention receives aninstruction to carry out image modification processing such as inversionprocessing or inside whitening processing, the image modificationprocessing is assuredly carried out on either the image signal on whichresolution correction using a small correction value has been carriedout or the image signal without resolution correction. Therefore, theproblem of an inversion noise caused by image modification processingcarried out on an image signal having been through resolution correctionwill be solved.

If the image modification processing is carried out on either an imagesignal with small amount of resolution correction or on an image signalwithout resolution correction in an area whose modification processinghas been instructed, a portion within the area, which should be invertedfrom black to white, can be processed without generating a black noiseand the resolution of the area outside the instructed one is corrected.Therefore, smear or degradation of optical resolution of letters in ahigh frequency portion outside the instructed area will not occur.

The configuration therefor is comparatively easy, which makes theindustrial value thereof high. The reason why so-called black noises arereduced or not generated after image modification processing such asinversion processing or inside whitening processing has been carried outon a binary converted image signal with weak MTF correction or no MTFcorrection thereon will be explained briefly.

FIG. 18(A) shows a table wherein data before MTF correction shown inFIG. 13(A) have been binary converted to white if the values are 50 orsmaller and to black if otherwise. As shown in FIG. 18(A), if no MTFcorrection has been carried out, the noise at the pixel K3 in FIG. 13(A)(having a value 60 while other pixels have 80) is not amplified and thepixel K3 is normally binary converted to a black pixel.

FIG. 18(B) shows a table of data which have been inverted from the datashown in FIG. 18(A), and FIG. 18(C) shows the data visually. Differentfrom FIGS. 14(B) and 14(C) which show the case where data after MTFcorrection are binary converted to white pixels if the values are 50 orsmaller and inverted thereafter, no black noise appears and theinversion processing has been carried out successfully.

On the other hand, FIG. 19(B) shows a table of data wherein the data inFIG. 18(A) have inside whitening processed, and FIG. 19(C) shows thedata visually. As a reference, FIG. 19(A) shows the same table as inFIG. 18(A). As in the case of the inversion processing above, no blacknoise appears and the inside whitening processing has been carried outsuccessfully, different from the case shown in FIG. 17 wherein binaryconversion to white if the values are 50 or smaller and inversionprocessing thereafter are carried out on the data after MTF correction.

In the above explanation, the case of binary conversion on an imagesignal without MTF correction has been described. In the case where thecorrection amount of MTF is reduced than in normal cases, the effectalmost the same is observed. This is because that the weaker the MTFcorrection is, the less an effect of noise signal amplification is.Therefore, conversion to black pixels is carried out normally.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a basic configuration of a first imageprocessing apparatus related to the present invention;

FIG. 2 is a block diagram (part 1) showing how correction amountchanging means in the first image processing apparatus is specificallyconnected;

FIG. 3 is a block diagram (part 2) showing how the correction amountchanging means in the first image processing apparatus is specificallyconnected;

FIG. 4 is a block diagram (part 3) showing how the correction amountchanging means in the first image processing apparatus is specificallyconnected;

FIG. 5 is a block diagram showing a basic configuration of a secondimage processing apparatus related to the present invention;

FIG. 6 is a block diagram showing a configuration of a first embodimentof an image processing apparatus related to the present invention;

FIG. 7 is a flow chart showing a flow of processing by a controlling CPUin the first embodiment of the image processing apparatus;

FIG. 8 is a block diagram showing a configuration of a second embodimentof an image processing apparatus related to the present invention;

FIG. 9 is a flow chart showing an operational flow of selecting means inthe second embodiment of the image processing apparatus;

FIG. 10 is a diagram showing a relation between the human visual senseand a ratio of black pixels in an area printed by a printer;

FIG. 11 is a diagram showing a general MTF correction method;

FIG. 12 is a diagram showing an example of inversion processing;

FIGS. 13(A) and (B) are diagrams showing MTF correction carried out on apredetermined image;

FIGS. 14(A) to (C) are diagrams showing an example wherein data afterMTF correction are binary converted and inverted thereafter;

FIG. 15 is a diagram showing an algorithm of inside whiteningprocessing;

FIGS. 16(A) through (F) are diagrams explaining the inside whiteningprocessing with reference to pixel patterns;

FIGS. 17(A) and (B) are diagrams showing an example wherein data afterMTF correction are binary converted and inside whitened thereafter;

FIGS. 18(A) to (C) are diagrams showing an example wherein data withoutMTF correction are binary converted and inverted thereafter; and

FIGS. 19(A) to (C) are diagrams showing an example wherein data withoutMTF correction are binary converted and inside whitened thereafter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, specific embodiments of image processing apparatusesrelated to the present invention will be explained with reference to theaccompanying drawings.

FIG. 1 is a block diagram showing a basic configuration of a first imageprocessing apparatus related to the present invention. In thisconfiguration, when no image modification processing is carried out, animage signal with resolution correction at a normal level (for example,MTF correction) is binary converted and output. When the imagemodification processing is instructed, either an image signal on whichweak resolution correction has been carried out or an image signal onwhich no resolution correction has been carried out is binary convertedand modification processing is then carried out thereon.

Various kinds of signal processing is carried out on an image signal S1by resolution correction means 200, correction amount changing means 300which changes the amount of resolution correction, and binary conversionmeans 400. Image modification processing such as inversion processing orinside whitening processing is then carried out on the signal by imagemodification processing means 500. The resolution correction means 200,the correction amount changing means 300, and the binary conversionmeans 400 may be connected in any manner as long as a signal input tothe image modification processing means 500 is the image signal havingbeen processed through weak resolution correction and binary conversionwhen the image modification processing is instructed. By the instructionto order image modification processing, a control signal CNT2 includinginformation showing an area to be processed by the image modification isinput to the image modification processing means 500. The imagemodification processing means 500 then carries out inversion processingor inside whitening processing on a binary signal S2 corresponding tothe area having been instructed. When no image modification is carriedout, the control signal CNT2 is not input to the image modificationprocessing means 500, and a signal without image modification processingis output from the image modification processing means 500.

The change of resolution correction amount by the resolution correctionmeans 300 may be carried out on an image signal corresponding to aspecified area by making a control signal CNT1 input to the correctionamount changing means 300 almost equal to the control signal CNT2.Alternatively, the correction amount may be changed for an image signalcorresponding to an entire image when the image modification processingis instructed.

By the configuration in the above, when no image modification processingis carried out, a signal which has been binary converted from the imagesignal with resolution correction at a normal level is output as it is,and when the image modification has been ordered, the processing iscarried out on a binary converted signal with weak resolution correctionor without resolution correction. Therefore, the problem of black noisescaused by image modification processing on an image signal whoseresolution has been corrected is solved.

FIGS. 2 to 4 are block diagrams showing specific connections between thecorrection amount changing means 300 and the binary conversion means400.

In an image processing apparatus shown in FIG. 2, correction amountchanging means 301 is configured so that it comprises resolutioncorrection means 201 and 202 using different resolution correctionamounts and selecting means 310 which selects a signal output fromeither the resolution correction means 201 or 202. Binary conversion iscarried out after the correction amount is changed by the correctionamount changing means 301. The selecting means 310 selects an imagesignal on which resolution correction has been carried out by theresolution correction means 201 (using a normal correction amount) whenno image modification processing is to be carried out. When imagemodification processing has been instructed, the selecting means selectsan image signal on which resolution correction has been carried out bythe resolution correction means 202 (using a small correction amount).The image signal having been selected by the selecting means 310 isbinary converted by binary conversion means 400 to produce a signal S2and image modification processing means 500 carries out imagemodification processing on S2. The resolution correction means 202 mayuse 0 as the correction amount, that is, it may not carry out resolutioncorrection. Alternatively, the image processing apparatus may notcomprise the resolution correction means 202 and the image signal S1 maybe input directly to the selecting means 310.

In the above configuration, one resolution correction means exists asthe resolution correction means 202. However, the number of theresolution correction means 202 may not be limited to 1, and a pluralityof resolution correction means using small correction values may beused. In this manner, the degree of resolution correction can be changedin smaller steps for processing such as inversion processing or insidewhitening processing which produces visual noises in various manner.This idea is the same for the configurations shown in FIGS. 3 to 5 whichwill be explained below.

In an image processing apparatus shown in FIG. 3, correction amountchanging means 302 comprises resolution correction means 201 and 202using different correction amounts, binary conversion means 401 and 402which respectively carry out binary conversion on signals output fromthe resolution correction means 201 and 202, and selecting means 311which selects a binary converted signal from either the binaryconversion means 401 or the binary conversion means 402. When no imagemodification is carried out, the selecting means 311 selects a signalhaving been binary converted by the binary conversion means 401 whoseresolution has been corrected by the resolution correction means 201(using a normal correction amount). When image modification processinghas been instructed, the selecting means 311 selects a signal havingbeen binary converted by the binary conversion means 402 whoseresolution has been corrected by the resolution correction means 202(using a small correction amount). The image modification processing iscarried out by image modification processing means 500 on the signalhaving been selected by the selecting means 311. In this configuration,the resolution correction means 202 may use 0 as the correction amount,that is, the resolution correction means 202 may not carry out anyresolution correction. Alternatively, the correction amount changingmeans 302 may not comprise the resolution correction means 202 anddirectly input an image signal S1 to the binary conversion means 402.

In an image processing apparatus shown in FIG. 4, correction amountchanging means 303 comprises resolution correction means 203 using avariable correction amount, and binary conversion is carried out afterthe correction amount has been changed by the correction amount changingmeans 303. The correction amount changing means 303 carries outresolution correction using a normal correction amount if no imagemodification processing is to be carried out, and carries out resolutioncorrection using a small correction amount when image modificationprocessing has been instructed. An image signal whose resolution hasbeen corrected by the resolution correction means 203 is binaryconverted by binary conversion means 400, and image modificationprocessing means 500 carries out the image modification processing onthe binary converted signal. The small correction amount used in theresolution correction may take 0.

In any one of the above image processing apparatuses, when imagemodification processing has been instructed, if the correction amountchanging means 300 to 303 inputs to the image modification processingmeans 500 the image signal SI for an entire image on which weakresolution correction has been carried out, or if the resolutioncorrection is carried out using a small correction amount on an imagesignal in an area specified by the instruction, image signals whereinresolution correction using the small correction amount has been carriedout on the image signal only in the area specified by the instructioncan be input to the image modification processing means 500.

FIG. 5 is a block diagram showing a basic configuration of a secondimage processing apparatus related to the present invention. Imagemodification processing is always carried out on an image signal withweak resolution correction. If no image modification processing has beeninstructed, a binary converted signal on which resolution correctionusing a normal correction amount has been carried out is selected, andan image signal on which image modification processing has been carriedout is selected if otherwise.

This image processing apparatus comprises resolution correction means201 and 202 using different correction amounts, binary conversion means401 and 402 which respectively carry out binary conversion on each ofthe signals output from the resolution correction means 201 and 202,image modification processing means 500 which carries out imagemodification processing on the binary converted signal from the binaryconversion means 402, and selecting means 321 which selects an imagesignal from either the binary conversion means 401 or image modificationprocessing means 500. The selecting means 321 selects a binary convertedimage signal on which resolution correction using a normal correctionamount has been carried out by the resolution correction means 201, whenimage modification processing is not to be carried out. When the imagemodification processing has been instructed, the selecting means 321selects an image signal which has been through weak resolutioncorrection by the resolution correction means 202, binary conversion,and image modification processing. In this configuration, the resolutioncorrection means 202 may use 0 as the correction amount, that is, theresolution correction may not necessarily be carried out. Alternatively,the image processing apparatus may lack the resolution correction means202, and the image signal S1 may be input directly to the binaryconversion means 402. In this manner, when no image modificationprocessing is carried out, a binary converted signal on which normalresolution correction has been carried out is selected, and when theimage modification processing has been instructed, a binary convertedand then image modified signal with weak or no resolution correction isselected. Therefore, by the image processing apparatuses shown in FIGS.1 to 4, the black noise problem due to modification processing on animage signal whose resolution has been corrected will be solved.

In the second image processing apparatus, as in the first one, aselecting signal from the selecting means 321 may select a signal onwhich image modification processing has been carried out correspondingto a specified area, by making a control signal CNT1 input to theselecting means 321 almost the same as the control signal CNT2.Alternatively, the selecting means 321 may select a signal on whichimage modification processing has been carried out for the entire imagewhen image modification processing has been instructed.

A more specific embodiment of the image processing apparatus related tothe present invention will be explained next. FIG. 6 is a block diagramshowing a portion composing the first embodiment of the image processingapparatus related to the present invention used in a stencil printerwherein a stencil making apparatus and a printer are unified. It isneedless to say that only the stencil making apparatus may be used, andthe block diagram in FIG. 6 can be used in the same manner in that case.

The image processing apparatus related to the first embodiment comprisestransfer means (in this case, a digitizer controlling CPU 82) whichtransfers a control signal 83 expressing whether or not an area to bemodified by inversion processing or inside whitening processing has beenspecified from image modification processing controlling means such as adigitizer (hereinafter called a digitizer unit 80) to this imageprocessing apparatus or to its controlling CPU 94. When the transfermeans show the image modification area specification of the inversionprocessing or the inside whitening processing, MTF correction isweakened or canceled before stencil making (before image modificationprocessing starts).

The image processing apparatus in the first embodiment adopts theconfiguration shown in FIG. 2. When stencil making including theinversion processing or the inside whitening processing is carried out,the MTF correction for the entire image is weakened or canceled.Therefore, a black noise can be prevented from being generated, and thesize of image processing apparatus is not large. When no inversionprocessing or inside whitening processing is carried out in the stencilmaking, high resolution image processing with MTF correction andprocessing by the digitizer except for the inversion processing or theinside whitening processing can be carried out in parallel. Hereinafter,the configuration and operation of the image processing apparatusrelated to the first embodiment will be explained in detail.

The image processing apparatus comprises an image sensor 10, such as aline image sensor, which obtains an analogue image signal S10 byscanning an original image (optical information) which is not shown, anA/D converter 12 which converts the analogue signal S10 to a digitalimage signal S12, correction amount changing means 30 which outputs acorrected signal S30 after carrying out MTF correction using differentcorrection amounts on the digital image signal S12 based on a selectingsignal S94, binary conversion means 40 which outputs a signal (binaryconverted signal) S40 after carrying out binary conversion on thecorrected signal S30 from the correction means 30 which is a multi-valuesignal, image modification processing means 50 which carries out imagemodification processing such as inversion processing or inside whiteningprocessing on the signal S40 output from the binary conversion means 40,a line thermal print head TPH90 which records image information on astencil master by using a heating element based on an output signal S56on which image modification processing has been carried out by the imagemodification processing means 50, a synchronization signal generatingcircuit 92 which generates synchronization signals S92 for synchronizingthe processing such as vertical scan synchronization signal, line (mainscan) synchronization signal, image synchronization signal, and imagevalidity signal, and a controlling CPU which controls the imageprocessing apparatus, and a printer and a stencil making unit which arenot shown in FIG. 6.

The correction amount changing means 30 comprises MTF correction means20 which carries out MTF correction on the digital image signal S12 andoutputs the corrected signal S20, and selecting means 32 which selectseither the corrected signal S20 from the MTF correction means 20 or thedigital image signal S12. The selecting means 32 selects either the MTFcorrected signal S20 or the digital image signal S12 based on aselecting signal S94. In the case without MTF correction (the selectingsignal S94 is OFF: 0), the digital image signal S12 is selected, whilein the case with MTF correction (the selecting signal S94 is ON: 1), theMTF corrected signal S20 is selected. The selected signal is output asthe output signal S30.

The selecting signal S94 is set by the controlling CPU94 which controlsthe image processing apparatus, and the printer and the stencil makingunit (not shown). A coordinate input circuit 81 in the digitizer unit 80transfers the coordinates of an area and image modification processingsuch as the inside whitening processing or the inversion processingspecified by a user of the image processing apparatus as a controlsignal S81 to the digitizer controlling CPU 82. Based on the controlsignal S81, the digitizer controlling CPU 82 determines the content ofthe image modification processing and the area to be processed. If theinside whitening processing and/or the inversion processing has beeninstructed, the digitizer controlling CPU 82 outputs a control signalS83 expressing the necessity of inversion or inside whitening processingto the controlling CPU 94. After receiving the control signal S83, thecontrolling CPU 94 sets the selecting signal S94 OFF before imagemodification processing is carried out on the binary converted signalS40. In this manner, when either the inversion processing or the insidewhitening processing is instructed, the digital image signal S12 withoutMTF correction thereon is selected as the output signal S30 from thecorrection amount changing means 30.

The digitizer controlling CPU 82 outputs the control signal S82 to amodification processing controlling circuit 85. Based on the content ofthe control signal S82, the modification processing controlling circuitcorrect 85 outputs a control signal S85 which controls an insidewhitening processing circuit in synchronization with the synchronizationsignal S92 and a control signal S86 which controls an inversionprocessing circuit. The control signals S85 and S86 include informationof a target area of the specified processing.

In this example, the digital image signal S12 without any correction canbe selected. However, MTF correction means 22 shown by a dotted line inFIG. 6 may be installed so that correction weaker than that of the MTFcorrection means 20 can be carried out thereby. In this manner, in thecase of no MTF correction (the selecting signal S94 is OFF: 0), thecorrection amount changing means 30 may select and output the signalfrom the MTF correction means 22.

Furthermore, either the digital image signal S12 or the corrected signalS20 may be selected based on the control signals S85 and S86 which willbe described later, instead of the selecting signal S94.

By selecting a signal based on the control signals S85 and S86, and bycarrying out binary conversion on image signals with strong and weak MTFcorrection, the binary converted signal with weak MTF correction isselected corresponding to the area on which the image modificationprocessing such as inversion processing or inside whitening processingis carried out, and the binary converted signal with strong MTFcorrection is selected in the case where no image processing is carriedout. In this configuration, even in the same stencil, a high resolutionimage with MTF correction can be used for the area except for theinversion processing area or the inside whitening processing area.

The image modification processing means 50 comprises line memories 51and 52 in the FIFO structure, an inside whitening processing circuit 54,and an inversion processing circuit 56.

The line memory 51 holds the binary converted signal S40 correspondingto 1 line (a main scan line). In synchronization with thesynchronization signal S92 from the synchronization signal generatingcircuit 92, the line memory 51 outputs a preceding line signal S51 andinputs the current line signal S40. The preceding line signal S51 outputfrom the line memory 51 is a line signal including a target pixel. Theline memory 52 holds the preceding line signal S51 corresponding to 1line (a main scan line). In synchronization with the synchronizationsignal S92 from the synchronization signal generating circuit 92, theline memory 52 outputs a signal S52 in the line before the precedingline and inputs the preceding line signal S51.

The inside whitening processing circuit 54 carries out the insidewhitening processing shown in FIG. 15 based on the signals S40, S51 andS52, and outputs an inside whitened signal S54. In response to thecontent of the control signal S82 from the digitizer controlling CPU 82in the digitizer unit 80, the inside whitening processing is carried outby the inside whitening processing circuit 54 according to the controlsignal S85 output from the modification processing controlling circuit85 in synchronization with the synchronization signal S92. The signal inthe line containing the upper pixel B in FIG. 15 is equivalent to thecurrent line signal S40, the signal in the line containing the targetpixel A and the neighboring pixels D and E is to the preceding linesignal S51, and the signal in the line of the lower pixel C is to thesignal S52 in the line before the preceding line. The selecting signal Jis equivalent to the control signal S85 output from the modificationprocessing controlling circuit 85 in the digitizer unit 80.

The inversion processing circuit 56 carries out the inversion processingshown in FIG. 12 and outputs an inverted signal S56. In response to thecontent of the control signal S82 from the digitizer controlling CPU 82in the digitizer unit 80, the inversion processing is carried out by theinversion processing circuit 56 according to the control signal S86output from the modification processing controlling circuit 85 insynchronization with the synchronization signal S92. The selectingsignal C in FIG. 12 is equivalent to the control signal S86 output fromthe modification processing controlling circuit 85 in the digitizer unit80.

FIG. 7 is a simple flow chart showing the flow of the processing by thecontrolling CPU 94 in the image processing apparatus having the aboveconfiguration. Hereinafter, the processing by the controlling CPU 94will be explained briefly.

The controlling CPU 94 confirms that a start key in an operation panel(not shown in FIG. 1) has been pressed down. If the start key has notbeen pressed down, it waits until the key is pressed. After the startkey has been pressed down, the controlling CPU confirms the controlsignal S83 expressing necessity of the inversion or inside whiteningprocessing. If the control signal S83 is OFF, it means that no inversionor inside whitening processing is necessary. The controlling CPU 94 thenoutputs 1 to make the selecting signal S94 ON, and switches theselecting means 32 to “with MTF correction”, and makes the selectingmeans 32 output the MTF corrected signal S20. On the other hand, if thecontrol signal S83 is ON, it means that inversion or inside whiteningprocessing is necessary. Therefore, the controlling CPU 94 outputs 0 tomake the selecting signal S94 OFF, and switches the selecting means 32to “without MTF correction” to make the selecting means 32 output thedigital image signal S12.

After switching the selecting means 32, the controlling CPU 94 carriesout stencil making operation or printing operation, and confirms thestart key pressed down again.

According to the first embodiment of the image processing apparatus,when image modification processing such as inversion processing orinside whitening processing has been instructed and in the case where anarea of image modification processing target has been specified, the MTFcorrection is weakened or canceled on the entire image signal before theimage modification processing starts. Therefore, according to the imageprocessing apparatus in the comparatively simple configuration, blackdots (noise) will not appear in the area of inversion processing orinside whitening processing. When stencil making without inversionprocessing or inside whitening processing is carried out, processing bythe digitizer except for inversion or inside whitening processing iscarried out in parallel to image processing on a high resolution imagewith MTF correction.

Referring to FIGS. 8 and 9, a second embodiment of the image processingapparatus related to the present invention will be explained next. InFIG. 8, elements the same as in FIG. 6 have the same indices and theirexplanation will be omitted here if unnecessary.

The image processing apparatus related to the second embodiment shown inFIG. 8 comprises binary conversion means 42 which carries out binaryconversion on an MTF corrected signal S20 on which strong resolutioncorrection has been carried out by MTF correction means 20, and binaryconversion means 44 which carries out binary conversion on an MTFcorrected signal S22 on which weak resolution correction has beencarried out by MTF correction means 22. Image modification processingmeans 60 carries out inversion processing or inside whitening processingon a binary converted signal S44 from the binary conversion means 44.Selecting means 70 is placed as a step succeeding the image modificationprocessing means 60. The image processing apparatus in the secondembodiment is different from the first one in these points describedabove.

The image processing apparatus in the second embodiment adopts theconfiguration shown in FIG. 5. When stencil making including inversionprocessing or inside whitening processing is carried out, a signal onwhich weak MTF correction and image modification processing have beencarried out is selected in response to an area on which the imagemodification processing such as inversion or inside whitening processingis carried out. When no image modification processing is carried out, abinary converted signal on which strong MTF correction has been carriedout can be selected. By this configuration, same as the firstembodiment, even in the same stencil, high resolution image with strongMTF correction (using a large correction amount) can be used for thearea except for inversion or inside whitening processing area.Hereinafter, the configuration and operation of the image processingapparatus related to the second embodiment will be explained in detail.

The image modification processing means 60 comprises line memories 61and 62 in the FIFO structure, an inside whitening processing circuit 64,and an inversion processing circuit 66.

The line memory 61 holds 1 line of the binary converted signal S44 withweak MTF correction (using a small correction amount). Insynchronization with a synchronization signal S92 generated by asynchronization signal generating circuit 92 the line memory 61 outputsa preceding line signal S61 and inputs a current line signal S44. Thepreceding line signal S61 output from the line memory 61 is a linesignal containing a target pixel. The line memory 62 holds a line ofsignal S61 which is preceding the line of the binary converted signalS44 with weak MTF correction. In synchronization with thesynchronization signal S92 output from the synchronization signalgenerating circuit 92, the line memory 62 outputs a signal S62 in a linebefore the preceding line and inputs the preceding line signal S61.

As in the first embodiment of the image processing apparatus, the insidewhitening processing circuit 64 carries out inside whitening processingshown in FIG. 15 using the signals S44, S61, and S62, and outputs aninside whitened signal S64. In response to the content of a controlsignal S82 from a digitizer controlling CPU 82 in a digitizer unit 80,the inside whitening processing circuit 64 carries out inside whiteningprocessing according to a control signal S85 output from a modificationprocessing controlling circuit 85 in synchronization with thesynchronization signal S92. The current line signal S44 is equivalent tothe signal in the line containing the upper pixel B in FIG. 15, thepreceding line signal S61 to the line containing the target pixel A andthe neighboring pixels D and E, and the signal S62 in the line beforethe preceding line is equivalent to the signal in the line containingthe lower pixel C. The selecting signal J is corresponding to thecontrol signal S85 output from the modification processing controllingcircuit 85 in the digitizer unit 80.

The inversion processing circuit 66 carries out inversion processingshown in FIG. 12 on the inside whitened signal S64 and outputs aninverted signal S56. The inversion processing circuit 66 operates in thesame manner as the inversion processing circuit 56 in the firstembodiment of the image processing apparatus.

A line memory 73 in the FIFO structure holds a line of the binaryconverted signal S42 with strong MTF correction. In synchronization withthe synchronization signal S92 from the synchronization signalgenerating circuit 92, the line memory 73 outputs a preceding linesignal S73 while inputting the current line signal S42. The line memory73 is used so that the signal S73 output from the line memory 73 is inthe same phase in the horizontal direction as the preceding line signalS61 output from the line memory 61 which contains the target pixel (thisphenomenon is called “synchronization of image signals”).

The selecting means 70, as in the first embodiment of the imageprocessing apparatus, selects either the signal S73 output from the linememory 73 or the signal S66 processed by the image modificationprocessing means 60, based on the control signals S85 and S86 outputfrom the modification processing controlling circuit 82. In the casewhere the control signals S85 and S86 are both OFF: 0, which means noinversion and no inside whitening processing, the selecting means 70selects the signal S73 output from the line memory 73. In the case wherethe control signal S85 is ON: 1, which means the necessity of insidewhitening processing, or in the case where the control signal S86 is ON:1, which means the necessity of the inversion processing, the selectingmeans 70 selects the signal S66 processed by the image modificationprocessing circuit 60. That is, the selecting means 70 selects thesignal S66 when either the control signal S85 or S86 is ON. By carryingout such processing on the signal for the entire image (on all pixels)which is the target of the processing, binary conversion is finished.The flow of operation carried out by the selecting means 70 is shownsimply in a flow chart in FIG. 9.

As has been described above, according to the second embodiment of theimage processing apparatus, the signal with weak MTF correction isselected in response to the area specified for the image modificationprocessing, when the image modification processing such as the inversionor inside whitening processing has been instructed. Therefore, the blacknoise problem due to the image modification processing on a signal withMTF correction will be solved and stencil making and printing can becarried out without generating black dots (noise) in the inverted orinside whitened area.

It is needless to say that not only weak MTF correction but no MTFcorrection, that is, the correction amount is 0, can be selected by thesecond embodiment of the image processing apparatus.

What is claimed is:
 1. An image processing apparatus comprising aresolution correction means for carrying out resolution correction on animage signal to improve spatial resolution of an image, a binaryconversion means for carrying out binary conversion on the image signalwhose resolution has been corrected by the resolution correction means,an image modification processing means for carrving out imagemodification processing based on a predetermined instruction to invertat least a portion of the image signal having been binary converted bythe binary conversion means, and a correction amount changing for meansmaking a correction amount of the resolution correction small based onthe predetermined instruction wherein the correction amount changingmeans comprises two resolution correction means which have differentcorrection amounts for the resolution correction and selecting meanswhich selects one of the image signals whose resolution has beencorrected by one of the resolution correction means, and, based on thepredetermined instruction, the selecting means selects the image signaloutput from one of the resolution correction means with a smallercorrection amount.
 2. An image processing apparatus comprising aresolution correction means for carrying out resolution correction on animage signal to improve spatial resolution of an image, a binaryconversion means for carrying out binary conversion on the image signalwhose resolution has been corrected by the resolution correction means,an image modification processing means for carrying out imagemodification processing based on a predetermined instruction to invertat least a portion of the image signal having been binary converted bythe binary conversion means a correction amount changing means formaking a correction amount of the resolution correction small based onthe predetermined instruction wherein the correction amount changingmeans comprises two resolution correction means which have differentcorrection amounts for the resolution correction, the binary conversionmeans comprises two binary conversion means which carry out binaryconversion on each of the image signals whose resolution has beencorrected by the resolution correction means, and selecting means whichselects one of the image signals having been binary converted by thebinary conversion means, and the selecting means selects the binaryconverted signal with a smaller amount of correction between the imagesignals whose resolution has been corrected by the two resolutioncorrection means, based on the predetermined instruction.
 3. An imageprocessing apparatus comprising a resolution correction means forcarrying out resolution correction on an image signal for improvingspatial resolution of an image, a binary conversion means for carryingout binary conversion on the image signal whose resolution has beencorrected by the resolution correction means, an image modificationprocessing means for carrying out image modification processing toinvert at least a portion of the image signal which has been binaryconverted by the binary conversion means based on a predeterminedinstruction, said resolution correction means includes two resolutioncorrection means using different correction amounts for the resolutioncorrection; and wherein said image processing apparatus comprises: twobinary conversion means for carrying out binary conversion on each ofthe image signals whose resolution has been corrected by the tworesolution correction means; said image modification processing meanscarries out image modification processing only on a binary convertedsignal with a smaller amount of resolution correction between the imagesignals whose resolution has been corrected by the two resolutioncorrection means; and selecting means which selects either the imagesignal on which image modification processing has been carried out bythe image modification processing means, or the binary converted signalwith a larger amount of correction between the image signals whoseresolution has been corrected by the two resolution correction means;said selecting means selecting the image signal on which the imagemodification processing has been carried out by the image modificationprocessing means based on the predetermined instruction.
 4. The imageprocessing apparatus as claimed in claim 3 wherein the selecting meansselects the image signal composing an entire image on which the imagemodification processing has been carried out by the image modificationprocessing means based on the predetermined instruction.
 5. The imageprocessing apparatus as claimed in claim 3 wherein, based on thepredetermined instruction, the selecting means selects a portion of theimage signal instructed by the predetermined instruction on which theimage modification processing has been carried out by the imagemodification processing means.